Investigation Of Characteristics Of Unregulated Emission From DMCC Engines

Methanol molecule contains oxygen atom and has no carbon-carbon double bond,and the production resouces of methanol are extensive,so it has been identified as a promising alternative fuel for diesel engine.Research showed that it could fully meet the demand of Euro V legislation without the help of seleted catalyst reduction（SCR）when the baseline Euro IV engine modified with DMCC technology and combined with after-treatment device DPOC（diesel oxidation catalyst（DOC）coupled with particulate oxidation catalyst（POC））.DMCC technology creates a low-cost route for heavy-duty diesel engine to meet Euro V legislation urea free.However,when compared with pure diesel mode,the unregulated emissions of DMCC engine on diesel methanol dual fuel（DMDF）mode increase to different degrees,especially at low load conditions.In order to obtain cleaner combustion of DMCC engine,based on our previous researches which only focused on unburned mentanol and formaldehyde emissions,the present research expands the unregulated emission investigation to carbon dioxide,nitrious oxide,formic acid,1,3-butadiene,benzene and toluene.Experiments have been carried out on two different heavy duty DMCC engines to investigate the unregulated emission characteristics and unregulated emission control method.The unregulated emissions from DMCC engine at different loads,speeds,methanol substitution ratios（MSRs）and diesel injection parameters were detected by FTIR method on line in our study.The conclusions of this study are as follows:The unregulated emissions（except CO₂）on DMDF mode increase to some extent when compared with pure diesel mode.Formaldehyde,unburned methanol,nitrous oxide,1,3-butadiene,formic acide,benzene and toluene emissions on DMDF mode are increased when compared with pure diesel mode,and they all increase with increasing MSR.However,CO₂ emissions decrease with the increase of MSR.With the increase of inlet temperature,formaldehyde,methanol,nitous oxide,1,3-butadiene,formic acid,benzene and toluene emissions descend at different MSRs,but CO₂ emissions ascend significantly.When EGR ratio increases,the formaldehyde,1,3-butadiene,formic aicd,benzene and toluene emissions of DMCC engine reduce gradually,but CO₂ emissions have the tendency to increase.The unregulated emissions of DMCC engine reduce with increasing rail pressure,advancing diesel injection timing and the application of pilot injection strategy.The increase of rail pressure shortens the fuel injection duration and promotes the atomization of fuel,thus increasses the premixed combustion ratio and leads to an increase in peak in-cylinder pressure and peak heat release rate,so the unregulated emissions reduce.With the advance of diesel injection timing,the premixed combustion ratio ascends and the ignition timing advances,thus prolongs the oxidation time at high temperature condition.As most of the unregulated emissions in our study belongs to incomplete combustion products except CO₂ and nitrous oxide,so the advance of injection timing could reduce the unregulated emissions which belong to incomplete combustion products.When compared with single injection strategy,the application of pilot injection strategy could help to raise the in-cylinder pressure and temperature before main combustion,so it could avoid the misfire combustion at low load conditions with high MSR.Furthermore,pilot injection could enhance the stability of engine and reduce most of unregulated emissions of DMCC engine.The conversion efficiency of DPOC for unregulated emissions tested in this research is quite high.Single DOC could significantly reduce the unburned methanol and 1,3-butadiene emissions from DMDF engine,especially at medium and high load conditions when exhaust gas temperature is relatively high,but formaldehyde emissions after DOC are increased at low load conditions.In general,the conversion efficiency of DPOC for unregulated emissions tested in this research is higher than that of single DOC,indicating that the catalyst（Pt）contained in POC facilitates the oxidation of unregulated gaseous emissions.The unregulated emissions between DMCC Euro V engine and baseline Euro IV diesel engine are not much different.After the catalysis of DPOC,the unregulated emissions of DMCC Euro V engine such as formaldehyde,methanol,1,3-butadiene,formic acid and nitrous oxide emissions are only slightly higher than that of baseline Euro IV diesel engine,and the CO₂,benzene and toluene emissions even lower than that of baseline Euro IV diesel engine.The combined application of DMCC technology and after-treatment device DPOC could not only help the regulated emissions of Euro IV engine to meet the demand of Euro V legislation urea free,but also realize low unregulated emissions as the unregulated emissions between DMCC Euro V engine and baseline Euro IV diesel engine are not much different.